摘要:
Vitellogenin (VTG) in zebrafish (Danio rerio) is a core biomarker for screening estrogenic activity of chemicals in the test guidelines of the Organization for Economic Co-operation and Development.Piscine VTG is normally quantified by the enzyme-linked immunosorbent assay (ELISA) including competitive ELISA and sandwich ELISA.Among them,competitive ELISA was the most commonly used method.To determine the optimal method for accurate quantification of zebrafish VTG,both competitive ELISA and sandwich ELISA were developed and their performances were compared in this study.First,VTG was purified from the whole body homogenate (WBH) of zebrafish treated with 17β-estradiol (E2)by gel filtration followed by anion-exchange chromatography.The purified proteins were subjected to native polyacrylamide gel electrophoresis (Native-PAGE) and stained positively with methyl green,Sudan black B,and Schiff's reagent,thus they were characterized as phospholipoglycoproteins.In sodium dodecyl sulfate-PAGE (SDS-PAGE),the purified proteins were separated into two major polypeptides corresponding to 180 and 143 kDa,which was similar to other reports on the VTGs.Therefore,the purified proteins were identified as zebrafish VTGs.Then,the purified VTGs were used to immunize rabbits by intraperitoneal injection to prepare anti-VTG polyclonal antibody.Western blot revealed that the prepared antibody reacted with homogenate from E2-treated male zebrafish and purified VTG,but no cross-reaction was observed in the homogenate from control male zebrafish,indicating that the antibody was highly specific to zebrafish VTG.Using the purified VTG and polyclonal antibody,competitive ELISA and sandwich ELISA for quantifying VTG concentrations in zebrafish were developed.The specificity test showed that VTG standard curves of both ELISAs were parallel to curves of WBH from E2-treated males,while there was no cross-reactivity with WBH from control males,confirming that both ELISAs could specifically quantify VTG concentrations of WBH in zebrafish.The competitive ELISA had a detection limit of 20 ng/mL and a working range from 31.25 to 1 000 ng/mL,while the sandwich ELISA had a working range from 3.9 to 250 ng/mL and a detection limit of 2.2 ng/mL,which was lower than the competitive ELISA.Moreover,the sandwich ELISA was simple and timesaving because it did not include the preincubation protocol of samples.Additionally,the intra-and inter-assay coefficients of variations in the sandwich ELISA were 2.1%~5.7% and 3.0%~7.3%,respectively,which were lower than the values of competitive ELISA,revealing that the sandwich format had a higher precision.This study revealed that the simple and highly sensitive sandwich ELISA was suitable for the accurate detection of VTG inductions in zebrafish exposed to environmental estrogens.%斑马鱼卵黄原蛋白(Vitellogenin,VTG)是检测环境雌激素活性的重要生物标志物.为了确定最佳的斑马鱼VTG检测方法,本研究利用纯化的斑马鱼VTG及其多克隆抗体同时建立了竞争ELISA与夹心ELISA,并比较了2种方法对VTG的敏感度与精确度.采用凝胶过滤与离子交换层析相结合的方法从17β-雌二醇暴露后的斑马鱼整体匀浆液中纯化获得了2种高分子量的糖磷脂蛋白,SDS变性电泳显示分子量为180与143 kDa的两条主带,证实纯化的蛋白为斑马鱼VTG.Western blot结果表明制备的抗血清对斑马鱼VTG具有很高的特异性,利用纯化的VTG及其多克隆抗体建立了定量斑马鱼VTG的竞争ELISA和夹心ELISA.与竞争ELISA相比,夹心ELISA不需要抗原抗体共孵育的过程,操作更加省时、简便,其工作范围为3.9~250 ng/mL,检出限约为2.2 ng/mL,组内与组间变异系数则分别为2.1~5.7和3.0~7.3,表现出更高的敏感度与精确度,推荐该方法用于环境雌激素活性的检测.